1. Field of the Invention
The invention relates to a transmission network in which switching orders are carried out in individual network nodes, and digital paths are switched in this way.
2. Description of the Prior Art
A transmission network of this type is shown in the Applicant's U.S. patent application Ser. No. 470,178, filed Jan. 25, 1990, entitled, "A Transmission Network Having Electronically Switchable Nodes for Switching Signal Paths and a Method of Controlling Said Network", said application being commonly assigned herewith and incorporated herein by reference. In the exemplifying embodiment of the invention shown therein, a digital path begins and ends outside the network nodes in multiplexers or demultiplexers.
However, a digital path, abbreviated hereinafter as DSV, can also begin or end within a network node. In this case, the input port of the source network node or the output port of the destination network node cannot be readily communicated to the other network nodes, as provided for in the Applicant's prior patent application.
An unambiguous designation of a DSV associated with a data signal address, hereinafter referred to as DS Address or `identification` and checking of the switching of these DSVs in the subsequent network nodes, is not possible in the prior application without special arrangements.
Another problem in the transmission network proposed in the prior patent application is the suppression of sequential alarms in network nodes, in the case of failure of a digital path.
It is desired that the digital signals be monitored in the switching distributors of the network nodes for the presence of a fault and that the failure of a DSV be reported from there to the controller of the network node or to a higher-ranking network management computer if available. The network node then releases an alarm, so that a substitute circuit can be established. If an alarm signal, AIS, received in a network nod were to be passed on transparently via several network nodes, then it would initially have to be assumed at each of these network nodes that the DSV failure occurred in the immediately preceding network section. Without special measures, each network node receiving an AIS would then release an alarm report to its controller or to the network management computer, and a regional substitute circuit could not be established, because a regional network management station could not detect in an unambiguous manner whether the fault was actually located in its areas of responsibility.